The present invention relates generally to corrosion protection through the use of a composition for providing a vapor phase corrosion inhibitor in a putty-like base to a substrate.
Corrosion is often a major problem during the transportation and storage of corrodible items, such as metallic articles. Metallic articles formed from iron, steel, copper, brass, aluminum, silver as well as other metals and alloys of such metals, are susceptible to corrosion. Corrosion can lead to tarnishing, discoloring or pitting of a metallic surface in the presence of oxygen and water. Because both oxygen and water are presently available under atmospheric and ambient conditions, precautions are necessary when packaging or storing such metallic items to prevent or minimize corrosive effects. Such corrosion oftentimes can occur after the manufacture of the articles, but prior to distribution to the ultimate consumer.
Conventional precautions for preventing corrosion include the use of volatile corrosion inhibitors (VCI) or vapor phase corrosion inhibitors (VPCI). These corrosion inhibitors react with a metallic surface to impede oxidation of the surface (anodic reaction) or to impede reduction of elementary oxygen to hydroxide ions (cathodic reaction). VCI and VPCI treatments require evaporation or sublimation of an inhibitor to provide a protective layer through deposition or condensation at the anodic or cathodic areas of a corrodible surface. Corrosion inhibitors work best in defined vapor spaces because to effectively treat metallic surfaces an adequate vapor pressure of the inhibitor should be achieved. A container or a wrapping material may be used to enclose a metallic object and form a vapor space into which the corrosion inhibitor may be located. Such container or wrapping material also acts as a barrier against atmospheric moisture from repeatedly contacting the metallic object.
In one known application a coating is purposely placed on an object with the intention of not being removed by the end user. Such a coating acts as a barrier to moisture and may contain a vapor phase corrosion inhibitor. For instance, European Patent Application EP/0,753,989 A1 discloses a conformal coating containing a vapor phase inhibitor for use with electronic circuit boards. The conformal coating is said to coat copper surfaces of the circuit boards with a vapor phase inhibitor offering protection against oxidation of the copper surfaces. A disadvantage of this technique is that a second coating is required to guard against small or pin-size holes in the coating that, when not covered, can lead to undesirable corrosion. Applying a second coating to protect against failure of a first conformal coating adds labor and material costs, as well as processing time and a discontinuity in the manufacture process, which can lead to making an otherwise moderate costing manufacture operation into an expensive one.
Another conventional technique for providing corrosion protection is to apply to a metallic surface a coating of a grease or paraffinic material that contains a vapor phase inhibitor. The material, when applied in a sufficiently thick layer, will act as a barrier to moisture, and the vapor phase inhibitor that is incorporated into this material will add further protection against corrosion. This technique, however, also suffers the disadvantage of being relatively expensive and inconvenient because the ultimate user typically removes the coating prior to use. Removal of the coating is often time-consuming and expensive.
To avoid the expense of removing a coating or the necessity of applying multiple coatings to achieve corrosion protection of a metallic surface, a vapor phase inhibitor may be included within a container or wrapping material that encloses a metallic object. U.S. Pat. No. 5,705,566 discloses a hot melt adhesive that includes particles of a vapor corrosion inhibitor mixed therein. The hot melt adhesive seals the flaps or seams of the container. A disadvantage of this technique is that corrosion protection of the metallic object placed within the container may be impaired because the inhibitor is not located on innermost interior surfaces of the container.
U.S. Pat. No. 5,715,945 discloses film packaging materials that contain vapor phase inhibitors. Such packaging materials can be used to wrap a metallic object to offer a protective barrier against atmospheric moisture. The vapor phase inhibitors mixed into these materials are intended to offer protection against corrosion of the metallic object enclosed within the packaging materials. This technique suffers from the disadvantage that the vapor phase inhibitor will often start to sublime after being mixed into the wrapping material, resulting in less available vapor phase inhibitor once the film is incorporated into an actual wrapping for the metallic object. After long periods of storage or transportation, the object may require fresh wrapping with material containing additional active vapor phase corrosion inhibitor. Often the wrapping material that contained the exhausted vapor phase corrosion inhibitor will have to be removed from around the metallic object. Such removal and re-wrapping of these materials is, especially for large metallic objects, time-consuming and expensive.
U.S. Pat. No. 4,973,448 discloses packets formed of sealed sheets of non-woven material that contain, among other things, a vapor phase inhibitor. Such packets are placed within a container or a wrapping film to provide corrosion protection of a metallic object placed therein. These packets may also contain a desiccant to further guard against moisture affecting the enclosed metallic object. As disclosed in U.S. Pat. No. 4,275,835, a package may have an adhesive layer on one of its outer surfaces for adhesively securing the package within an enclosure. A disadvantage of these prepackaged vapor phase inhibitors is that the packing of the inhibitors into the non-woven material is expensive and time-consuming. Furthermore, surfaces within cavities of a metallic object often demand special consideration for corrosion protection because such cavities create harbors where moisture can collect. Such prepackaged packets of vapor phase corrosion inhibitors are often sized too large to be placed within cavities of a metallic object because as the size of the packets are reduced the cost of the packaging of the packets increases relative to the cost associated with the vapor phase inhibitor contained therein.
While conventional techniques offer some protection against corrosion, they suffer from the disadvantages previously described. As such, there is a need for a simple, easy to use product that prevents corrosion and that can be easily be applied within protective barriers.
The present invention provides compositions which include a releasable vapor phase corrosion inhibitor for protecting metallic substrates against corrosion. These compositions are capable of both direct and indirect contact with metallic objects. The present invention also provides for methods of preparing the compositions, articles of manufacture and methods of producing them.
The compositions of the present invention include a base material that is pliable and has sufficient tackiness to be securely affixed to surfaces. This base material can be described as having physical characteristics of a putty or putty-like material. The base material includes a releasable vapor phase corrosion inhibitor which sublimes or evaporates and offers corrosion protection to metallic surfaces within an enclosed vapor space that is not in direct contact with the inventive compositions.
Examples of the base materials useful in the inventive compositions include silicones; fluorosilicones; polyurethanes; polysulfides; polybutylenes (polymers based on C4 monomers); polyvinyl chloride; acrylic resins; vinyl acetate; ethylene vinyl acetate; vinyl acrylic (copolymers of vinyl acetate and alkyl acrylates such as butyl acrylate); styrene butadiene rubber (SBR); styrenic block copolymers; oleoresinous compositions; bituminous; rosin; unsaturated elastomers such as polybutadiene, polyisoprene and polychloroprene; and saturated elastomers such as polyisobutylene, ethylene propylenediene monomer rubber (EPDM), ethylene-propylene copolymers (EPRxe2x80x94Ethylene Propylene rubber), nitrile-butadiene rubber, and polybutene.
The pliability and tackiness of the base material allows the present invention to be used to offer corrosion protection to cavities of metallic objects. The inventive compositions can be placed over surfaces proximal to the cavity to guard against moisture reaching locations within the cavity. The corrosion inhibitor releasably contained in the base protects the metallic surfaces within the cavity.
The corrosion product of the present invention may also be used as a temporary coating to provide direct contact corrosion protection. The base material of the present invention can be easily removed from metallic surfaces without leaving undesirable residues of material.
Certain useful corrosion inhibitors of the present invention include sodium nitrite, dicyclohexylamine, sodium benzoate, hexadecylpyridinium iodide; dodecylbenzyl quinolinium bromide; propargyl quinolinium bromide; cyclohexylammonium benzoate; ammonium benzoate; dicyclohexylammonium nitrite and dicyclohexylamine chromate, benzotriazole; sodium dinonylnaphthalene sulfonate; triethanolamine dinonylnaphthalene sulfonate; calcium dinonylnaphthalene sulfonate; magnesium dinonylnaphthalene sulfonate; barium dinonylnaphthalene sulfonate; zinc dinonylnaphthalene sulfonate; lithium dinonylnaphthalene sulfonate; ammonium dinonylnaphthalene sulfonate; ethylenediamine dinonylnaphthalene sulfonate; diethylenetriamine dinonylnaphthalene sulfonate and 2-methylpentanediamine dinonylnaphthalene sulfonate; sodium molybdate, or their salts and combinations thereof.
In certain embodiments of the present invention, the corrosion protection product includes a moisture absorbing compound to further guard against corrosion. Such moisture-absorbing compound can also contain an indicator revealing a color change when the moisture absorbency of the compound is utilized. Such a color change can indicate that additional product may be applied to maintain adequate levels of corrosion protective material.
One advantage of the present invention is that it provides a composition and delivery vehicle for corrosion inhibitors which is cost efficient, easy to use and can be conveniently removed or replaced.